iio: mxs-lradc: Do hardware initialization earlier

We need to initialize hardware before registering the touchscreen. Else,
we end up setting registers in mxs_lradc_ts_open(), getting called just
after registering the touchscreen with input_register_device() and by
the end of mxs_lradc_probe(), we reset the LRADC block hence losing the
correct configuration.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Cc: Fabio Estevam <fabio.estevam@freescale.com>